1. Field of the Invention
The present invention relates generally to multi-purpose athletic shoes and, more particularly, to athletic shoes with interchangeable/detachable rear soles that provide extended and more versatile life and better performance in terms of cushioning and spring.
2. Discussion of the Related Art
Athletic shoes, such as those designed for running, tennis, basketball, cross-training, hiking, walking, and other forms of exercise, typically include a laminated sole attached to a soft and pliable upper. The sole usually includes an abrasion-resistant, rubber outsole attached to a cushioning midsole usually made of polyurethane, ethylene vinyl acetate (EVA), or a rubber compound.
One of the principal problems associated with athletic shoes is wear to both the outsole and midsole. A user rarely has a choice of running or playing surfaces, and asphalt and other abrasive surfaces take a tremendous toll on the outsole. This problem is exacerbated by the fact that, with the exception of the tennis shoe, the most pronounced outsole wear for most users, on running shoes in particular, occurs principally in two places: the outer periphery of the heel and the ball of the foot, with heel wear being, by far, a more acute problem because of the great force placed on the heel during the gait cycle. In fact, the heel typically wears out much faster than the rest of the athletic shoe, thus requiring replacement of the entire shoe even though the bulk of the shoe is still in satisfactory condition.
Midsole wear, on the other hand, results not from abrasive forces, but from repeated compression of the resilient material forming the midsole due to the large force exerted on it during use, thereby causing it to lose its cushioning effect. Midsole compression is also the worst in the heel area, particularly the outer periphery of the heel directly above the outsole wear spot and the area directly under the user's calcaneus or heel bone.
Despite higher prices and increased specialization, no one has yet addressed heel wear problems in an effective way. To date, there is nothing in the art to address the combined problems of midsole compression and outsole wear in athletic shoes, and these problems remain especially severe in the heel area of such shoes.
Designs are known that specify the replacement of the entire outsole of a shoe. Examples include those disclosed in U.S. Pat. Nos. 4,745,693, 4,377,042 and 4,267,650. These concepts are impractical for most applications, however, especially athletic shoes, for several reasons. First, tight adherence between the sole and the shoe is difficult to achieve, particularly around the periphery of the sole. Second, replacement of the entire sole is unnecessary based upon typical wear patterns in athletic shoes. Third, replacing an entire sole is or would be more expensive than replacing simply the worn elements, a factor which is compounded if a replaceable, full-length sole for every men's and women's shoe size is to be produced. Finally, it would appear that the heel section, in particular, has entirely different needs and requirements from the rest of the shoe sole which derive in substantial part from its rate of deterioration.
Other designs, which are principally directed to shoes having a relatively hard heel and outsole (e.g., dress shoes), disclose rear soles that are detachable and which can be rotated when a portion of the rear sole becomes worn. Such designs, however, have never caught on in the marketplace because it is simply too easy and relatively inexpensive to have the entire heel on such footwear replaced at a commercial shoe repair shop.
It is difficult to adapt such "dress shoe" designs to athletic shoes for various reasons. One reason is that the soft, resilient materials utilized in athletic shoe soles make it extremely difficult to devise a mechanism for detachably securing heel elements to each other without adversely affecting the cushioning and other desired properties of the shoe. On the other hand, utilization of hard materials in athletic shoes tends to increase weight and decrease comfort and performance.
For example, U.S. Pat. No. 1,439,758 to Redman discloses a detachable rear sole that is secured to a heel of the shoe with a center screw that penetrates the bottom of the rear sole and which is screwed into the bottom of the heel of the shoe. Such a design cannot be used in athletic shoes because the center screw would detrimentally affect the cushioning properties of the resilient midsole and may possibly be forced into the heel of the user when the midsole is compressed during use. Furthermore, a center screw does little for peripheral adherence of the sole to the shoe heel in the case of resilient materials.
Another truism in the athletic shoe industry is that, while cushioning has received a lot of attention, spring has received very little, despite the fact that materials like graphite and various forms of graphite composite possess the proper characteristics for spring enhancement without increasing weight. One reason may be the perceived tendency of graphite or graphite composite to crack under stress. Yet another reason may be the increased cost associated with such materials. Yet another reason may be that the tremendous variation in body weight and spring preference of would-be users makes it commercially unfeasible to mass-market athletic shoes with graphite spring enhancement, given the countless options that would have to be offered with each shoe size. Since heel spring is largely ignored, it goes without saying that spring options are also non-existent.
Also absent from the marketplace are truly multi-purpose athletic shoes. Notwithstanding a few "run-walk," "aerobic-run," and all-court models, the unmistakable commercial trend appears to be increased specialization, with no apparent industry awareness of the fact that the use and function of an athletic shoe can be changed dramatically if it is simply given interchangeable rear soles. Similarly, no athletic shoe manufacturer has yet to offer varying heel cushioning firmness in each shoe size, despite the fact that consumer body weight for each shoe size spans a huge spectrum. While a few manufacturers offer width options in shoe sizes, varying firmness of cushioning in a single model or shoe size is nonexistent in the marketplace.